In the operation of multi-fuel systems for engines, it is necessary to identify the fuel being used and then appropriately change the volume of fuel entering the combustion chambers and the timing of the engine. Examples of such systems are set forth in Oliver Phillips U.S. Pat. No. 4,594,201 which issued Jun. 10, 1986 and Carlo Casacci U.S. Pat. No. 4,922,862 which issued May 8, 1990.
Spark ignition Otto cycle "Flexible-fueled" or "Variable-fueled" engines use a sensor to identify the fuel type along with the well known closed-loop system which senses the oxygen content of the engine exhaust to maintain a desired fuel/air ratio for the engine. Given an accurate and stable sensor for determining the characteristics of the fuel being used at any instant, it is a reasonably simple matter to control the carburetor or other means which might be used for introducing the fuel into the inlet air, even if the fuel characteristics vary rapidly during operation due to incomplete mixing in the fuel tank.
The problems are much greater when attempting to provide similar automatic control of a multi-fuel or flexible-fueled diesel cycle engine as is the subject of this invention. In this type of engine, certain characteristics of the fuel being delivered from the tank which will provide an indication of the fuel volumetric energy content must also be automatically sensed by a suitable fast acting sensor because the fuel characteristics may change rapidly due to incomplete mixing of two fuels, such as methanol and diesel fuel, in the fuel tank or when changing over from one fuel to another if two fuel tanks are used. Signals from the sensor are delivered to the engine control system. In addition, the fuel is injected at high pressures using a separate fuel pump for each cylinder which can thus be spaced apart as much as the length of the engine but which must each inject about the same amount of fuel energy at the correct time in the engine cycle. Consequently, means must be provided to assure that each of the high pressure pumps are fed with fuel having essentially the same characteristics at any given time.
The present invention is directed to overcoming one or more of the problems as set forth above.